Males and females between the ages of 20-80 are eligible for study. Women must be either at least one year post-menopausal, or using an adequate contraceptive method for at least one month prior to and during participation in this study. All will carry the diagnosis of idiopathic Parkinson's disease based on the presence of a characteristic clinical history and neurological findings. All will have relatively advanced disease with levodopa-associated motor response complications, including peak-dose dyskinesias and wearing-off fluctuations.